The present invention refers to a device in gas lasers, especially so called white light lasers and of the kind which at one hand comprises at least one gas discharge tube in the form of an electrode segment comprising at least one cathode electrode arranged between anode electrodes, the electrode surfaces of said cathode electrode being exposed to the gas and on the other hand comprises end members enclosing the gaseous medium within the segment.
Hollow cathode lasers are a special type of gas lasers in which the active area consists of the negative plasma glow. The lazing substance is often a metal ion excited in a rare-gas plasma, but lazing in pure rare-gas mixtures also occurs. Of special interest are He-Cd hollow cathode lasers, since they can laze continuously and simultaneously in red, green and blue. Such lasers, so called white light lasers, are interesting i.a. at handling of colour pictures.
Many constructions of white gas lasers have been tested, but yet there are none that are commercially available. This probably depends on life- and instability problems. The life limit is primarily caused by the fact that the metal vapour is diffused from the active areas and e.g. is deposited on the Brewster window or--if such are missing on--the laser mirrors. The instability of laser output is primarily caused by plasma instabilities. These are generated e.g. by temperature gradients in the laser, geometry deficiencies and presence of undesired substances in the laser cavity.